The present invention relates in general to cylinder type key locks, and more particularly to key-operated rotary plug cylinder locks having rotary disc type tumblers and having special provisions for protecting the same against detection of the distinctive key contour or combination surface by picking probes or the like and otherwise enhancing protection of the lock against unauthorized entry.
One of the common types of key locks which have come into wide is the type known as a cylinder lock. Conventional cylinder locks normally comprise a relatively fixed cylinder forming the lock body or casing having a cylindrical bore opening through the front surface of the lock body which rotatably houses a rotating plug assembly. The rotating plug assembly has a key way or key slot opening through the front surface of the plug and extending over most of the axial length of the plug, as well as one or more resiliantly urged tumblers formed of rotatable or slidable members which normally occupy positions confronting surfaces or traversing sheer planes or interfacial planes preventing rotation of the plug relative to the cylinder. When a key of proper contour or combination surface is inserted in the key way or key opening in the plug, the contoured key surface aligns the resiliantly urged tumpler members in such a way that a parting line, either of the tumbler members or of some other locking member coactive with the tumbler members, is brought into coincidence with the interfacial plane or the arcuate peripheral surface of the plug, so that when all of the resiliantly urged tumblers are properly aligned by the contoured key surface, rotational motion imparted to the key permits the plug to turn through the normal motion involved in moving the lock from a locked to an unlocked condition.
Due to conditions which arise in the construction of the lock parts under normal manufacturing tolerances, it has been possible in cylinder locks which are not provided with special pick resistant features, to achieve unauthorized operation of the lock by such picking techniques as inserting a picking tool into the key way and exerting a torque on the plug so that with careful movement of the plug in selected directions, the resiliantly urged tumbler first placed in compression by torquing the plug is aligned by the pick for clearance, at which point the plug rotates a minute degree to bring the next resiliantly urged tumbler into a similar compressed condition and is aligned by the pick for clearance, and this succession of operation is repeated until all of the tumblers have been aligned to permit the plug to be rotated.
One of the most common types of cylinder locks is the pin tumbler type cylinder lock, wherein segmented tumbler pins formed of lower key engaging pin segments and upper drive pin segments have a line of separation between the segments which is normally displaced from the shear line of the plug but is positioned by the proper key so that the line of separation of all of the pin tumblers align with the plug shear line and permit rotation of the plug. Such pin tumbler type cylinder locks have been particularly susceptible to the above described types of picking techniques, and many attempts have been made to provide them with resistance to such picking operations. In some cases, the pin tumblers have been so constructed that the tampering by picking techniques with one of the tumbler pins automatically locks the remaining tumblers against further movement, or additional recesses have been provided in the outer cylindrical casing so that after a pin tumbler has been picked it re-engages in the absence of clearance of the remaining pin tumblers, or lock out devices have been provided so that attempts to pick one or more of the pin tumblers results in additional locking pins being activated to lock the plug against rotation even by authorized persons.
To increase resistance to picking by the techniques which are successful with pin tumbler type cylinder locks, cylinder locks of the rotary disc tumbler type have come into wider use. A popular type of rotary disc tumbler cylinder lock is the so-called Abloy lock, wherein a bank of peripherally gated rotary locking discs housed within a rotatable sleeve member have shaped center apertures which respond to a proper key surface to align the gates to permit radially inward movement of a locking bar which normally traverses the shear line between the rotary sleeve and an outer fixed cylinder casing. Such rotary disc tumbler type cylinder locks may be of the general type disclosed in U.S. Pat. No. 3,771,340 or 3,621,689, or 3,848,442, with or without related features of other patents obtained by the Finnish corporation Oy Wartsila Ab relating to the Abloy lock. Unauthorized detection of such rotary disc tumbler cylinder locks has been achieved, however, by techniques such as introducing a picking probe or similar tool into the key opening to interpose an offset shaped extension thereof between the faces of successive rotary disc tumblers and manipulating the probe to detect the position of the key engaging shoulder formation of the respective tumblers and by observing the angular position of the probe externally of the lock determine therefrom the key combination or shaped surface contour of the key for that lock. Also, techniques of torquing the plug of such locks in a special manner or driving the center portion of the plug axially inwardly or drilling through the front of the lock case in alinement with the locking bar permitting removal of the locking bar have resulted in unauthorized penetration of the lock.
An object of the present invention is the provision of a novel rotary plug cylinder lock having rotary disc type tumblers constructed in a special manner to resist unauthorized detection of the key combination for the lock and resist unauthorized penetration of the lock.
Another object of the present invention is the provision of a novel rotary plug cylinder lock of the rotary disc tumbler type having the disc tumblers shaped to provide portions which internest in recessed formations in the adjacent tumbler disc and resist penetration of detecting probes into inter-tumbler spaces which would reveal the key combination for the lock.
Another object of the present invention is the provision of rotary plug cylinder locks of the type described in either of the two immediately preceeding paragraphs wherein disabling features are incorporated in the lock for preventing penetration or unauthorized operation of the lock when the plug or portions thereof are subjected to excessive stresses in certain directions.
Other objects, advantages and capabilities of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings illustrating a preferred embodiment of the invention.